Re: [GIT PULL] tracing/kprobes: Add dynamic tracepoints + instructiondecoder

From: Masami Hiramatsu
Date: Thu Aug 27 2009 - 13:29:35 EST

Frederic Weisbecker wrote:
On Thu, Aug 27, 2009 at 11:00:38AM -0400, Masami Hiramatsu wrote:
Frederic Weisbecker wrote:

This is the kprobes tracing pile of patches. I've tested it
successfully by setting some kprobes through debugfs by hand.

It brings no known regressions.

However, the stress test provided by Masami have revealed some
unstable points. Some symbols are unsafe to probe and raise
probing recursion.

I've added a tiny patch in the series that helps identifying the
kprobe that has raised such situation.
For example it has learned me today that it's unsafe to trace
ret_from_exception() (obviously: it's on the int 3 handler path).

Thank you, Frederic.

I'm currently fixing those problems on x86-64 (on kvm).
I'll also check it on x86-32, and fix it.


Don't hesitate to interate through small patches that fix these

So that I can continue to test it over time and report you what I find,
may be I can try to fix some of them too.

I haven't fixed ret_from_exception because I wasn't sure about the
right thing to do: putting it in the kprobes section or blacklist its
name. It's a bit more delicate to put assembly code into sections so... :)

It depends on implementation, but I think blacklist is the last resort. :)
AFAIK, some assembly codes are already pushed into kprobes section.

Thank you,

Masami Hiramatsu

Software Engineer
Hitachi Computer Products (America), Inc.
Software Solutions Division

e-mail: mhiramat@xxxxxxxxxx

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